Electrolytic cell having adjustable anode sections

ABSTRACT

This invention provides an anode assembly having movable anode sections for use in Hooker-type electrolytic cells. Movement of the anode sections enables the width of the anodes to be adjusted which decreases many of the problems encountered during assembly of the electrolytic cell and also permits minimizing the distance between the anode and the diaphragm surface on the cathode.

I United States Patent [1 1 [111 3,803,016 Conner, Jr. Apr. 9, 1974 ELECTROLYTIC CELL HAVING 3.498.903 3 1970 Kamarjan 204/286 ADJUSTABLE ANODE SECTIONS 3,591,483 7/l97l Loftfield et al. 204/252 3,579,431 5/l97l Jasberg 204/280 [75] Inventor: Frank E. Conner, Jr., Charleston,

Primary Examiner-John H. Mack [73] Assignee: FMC Corporation, New York, AS81310"! omon [22] Filed: Feb. 9, 1972 ABSTRACT [2]] Appl 224314 This invention provides an anode assembly having movable anode sections for use in Hooker-type elec- [52] US. Cl 204/286, 204/252, 204/266 trolytic cells. Movement of the anode sections enables [51] Int. Cl C23b 5/68 h idth f h nodes to be adjusted which de- [58] Field of Search 204/252, 266, 280, 286 creases ny f h problems encountered during assembly of the electrolytic cell and also permits mini- [56] Ref Cit d mizing the distance between the anode and the dia- UNITED STATES PATENTS phragm surface on the cathode. 3,674,676 7/l972 Fogelman 204/252 2 Claims, 3 Drawing Figures SECTION A-A CATHODES PATENTEBAPR 9 1974 $803,016

SHEEI 1 OF 2 FIG.

SECTION A-A (WITHOUT CATHODES) FIG. 2

CATHODES SECTION A-A PATENTEUAFR 91924 v 3.8031116 SHEET 2' [IF 2 ELECTROLYTIC CELL HAVING ADJUSTABLE ANODE SECTIONS This invention concerns electrolytic cells of the Hooker-type which consist essentially of a cell enclosure, an anode of chlorine-resistant electro-conductive material, such as platinum group metals or their oxides coated on titanium, a foraminous cathode, usually made of iron and a porous diaphragm of asbestos or like material which is placed in the anode-cathode gap to provide an anode compartment and a cathode compartment.

In the normal construction of such cells, the diaphragm is in direct contact with the cathode. Frequently, the diaphragm is deposited on the cathode by placing the cathode in an aqueous slurry of asbestos and causing the slurry to flow through the pores or mesh openings of the cathode until a porous sheet or layer of asbestos has been deposited upon the side of the cathode which in use is opposite the anode.

Electrolytic cells employing a porous diaphragm between the anode and cathode are widely used in the production of chlorine and caustic alkali by the electrolysis of an alkali metal chloride solution. Generally these diaphragm-type electrolytic cells can be divided into two types:

1. bipolar cells such as the cell described in US. Pat. No. 3,242,059 in which both the anode and cathode contact the diaphragm (no gap between anode and diaphragm), and

2. conventional cell (Hooker-type), that is a diaphragm cell in which a gap is maintained between the anode and the diaphragm. As used herein, the term Hooker-type cell, refers to all conventional type cells with a formed in place diaphragm.

In the Hooker-type cell, the anode is usually graphite or a dimensionally stable metal electrode and the cathode is usually foraminous iron or steel. The cells contain a plurality of anodes and cathodes. The anodes are fixed to a cell base and are spaced apart so that the cathodes can be alternated between the anodes.

When the Hooker-type cell is used to produce chlorine, an alkali metal chloride solution is used in the cell as the electrolyte. As current is passed through the electrolyte between the anode and cathode, chlorine is evolved at the anode and alkali metal ions are discharged at the cathode which ions react at the cathode base with water from the electrolyte to form caustic alkali and liberate hydrogen. A porous diaphragm is placed in the anode-cathode gap in order to prevent as far as possible, mixing of the hydrogen with chlorine and mixing of the caustic alkali with the incoming brine which is fed to the anode side of the diaphragm.

In the Hooker-type cells, it is desired to keep the anode-cathode gap small since the resistance of the electrolyte in the gap to the passage of the electrolyzing current raises significantly the operating voltage of the cells and consequently increases the energy consumption and decreases power efficiency.

With conventional Hooker-type cells, the anodecathode gap cannot be reduced below a certain minimum distance. Substantial space is required during assembly of the cell, between the anode and the cathode to prevent scraping between them caused by dimensional deviations or misalignments of the anodes and cathodes. Scraping between the anode and cathode must be avoided because it results in breaking of the diaphragm which causes operating problems due to mixing of the anodic and cathodic products.

Furthermore, during operation of the cell as a chlorine cell, a gap between the anode and the diaphragm facilitates the passage of chlorine evolved at the anode and the replenishing of the brine solution in contact with the anode. If this gap is too small during operation of the cell, the diaphragm may become ineffectivedue to insufficient brine flow, the formation of gas pockets or hot spots.

Despite the problems that may occur when the gap between the anode and diaphragm is reduced, commercial installations attempt to minimize the gap between the anode and diaphragm because reduction of this gap results in considerable savings in energy consumption due to the reduction in the resistance to current flow and concurrent lowering of cell voltage.

When a conventional Hooker-type cell is assembled containing a plurality of fixed anodes arranged vertically in a regular pattern with spaces between each anode and a corresponding pattern of fixed cathode fingers which fit between the spaces of the anodes, the minimum gap between the anode and cathode is usually approximately one-half inch. The magnitude of this gap is mainly required for assembly of the cell to allow for misalignment or dimensional irregularities of the anodes and cathodes since a gap of less than one-half inch would be adequate for cell operation. These misalignments and dimensional irregularities are caused by dimensional tolerances in constructing the anode and cathode assemblies and subsequent dents, deformities or warping of the cathode fingers or dimensionally stable anodes which occur during assembling and disassembling of the cells despite great care. Even with a gap of about one-half inch, great care is required in lowering the cathode assembly between the anodes to prevent scraping off the diaphragm which is difficult and time consuming and thereby raises the cost of assembly.

This invention, described in summary form, provides a novel anode structure having adjustable anode sections for use in a Hooker-type cell and a method of assembling a Hooker-type diaphragm cell employing the novel anode structure which minimizes the gap between the anode and the cathode. The novel anode structure comprises; a base plate, a pluralityof essentially parallel dimensionally stable metal anodes, each of said anodes having adjustable sections and each section having an anode mount for attaching the anode section in an essentially perpendicular position to the base plate and said anode mount having means for providing two modes of attaching the anode section to the base plate, the first mode in which each anode section is movably attached to the base plate permitting horizontal movement of the anode sections in relation to the base plate for varying the width of the anode composed of said sections, and a second mode in which each metal anode section is rigidly attached to the base plate.

This invention also provides an improved method of assembling a Hooker-type diaphragm cell employing the novel anode structure characterized by having a cell can, a cell base plate, an anode of chlorineresistant electroconductive material having movable sections for varying the width of the anode, a foramin'ous cathode, a porous diaphragm between the anode and cathode and a gap between the anode and the cathode, wherein the improvement comprises the following steps:

a. mounting the essentially vertical and parallel metal anodes to the essentially horizontal cell base plate;

b. adjusting sections of each metal anode to minimize the width of the anode and thereby maximize the gap between anodes for inserting cathodes;

c. inserting the essentially vertical cathodes and the diaphragm between the anodes;

d. positioning the anode sections to reduce the gap between the anodes and the cathodes to any desired distance by increasing the width of the anode; and

e. fixing the anode sections in the position of reduced gap obtained in step d. I

FIG. 1 is a simplified side view of the novel anode structure.

FIGS. 2 and 3 are simplified side and top views respectively of a typical Hooker-type diaphragm cell partially assembled with the anode sections adjusted to maximize the gap and with the cathodes in a partially inserted position. The cell can has been removed for clarity.

Specifically this invention provides a novel anode structure for use in a Hooker-type diaphragm cell and an improved method of assemblinga Hooker-type diaphragm cell. The novel anode structure includes variable width anodes having adjustable anode sections. The width of the anode is varied by movement of the anode sections with respect to the cell base. The anode section has amount which permits such movement.

The term anode as used herein refers to the electrode between adjacent cathodes. The variable width anode of the instant invention is therefore comprised of movable anode sections which are located between adjacent cathodes.

The interrelationship between the structural configuration of the anode mount and the base must be such that the anode mount and anode sections can move parallel with respect to the plane of the base when the anode mount is in a first mode and the anode mount and anode sections must be fixed to the base to prevent lateral motion when the anode mount is in the second mode. This movement of the sections of an anode permits adjusting the width of the anode. When the anode mount is in the first mode, sections of the anode should be free to move at least one thirty-second of an inch and preferably about three-fourths of an inch.

With reference to FIG. 1, this interrelationship between the structural configuration of the anode mounts and the base is preferably obtained as follows;

a cell base plate 10, having disposed therein a number of holes 12, (preferably slots) through which anode mounts l4 protrude; the anode mount 14, is a stud having a diameter sufficiently smaller than hole 12, in cell base plate 10, to permit about three-fourths inch lateral movement of a section 16 of anode 18, attached to the stud; and a nut 20, larger than the hole in the cell base plate is threaded onto the end of stud 14, protruding through the hole. A washer 22, is usually inserted between the nut 20, andthe cell base plate 10. A collar 24 to facilitate sliding of the anode sections is preferably attached to the stud above the base plate. The first mode is achieved with the nut 20, loosely threaded onto the stud 14, to permit lateral sliding of the stud in the hole. The second mode is achieved by tightening the nut to secure it against, thebase plate. A gasket, 26; placed above the base plate, insulates the base from the anolyte and seals the slot opening in the base by being compressed between the collar and the base.

The studs and collars are preferably staggered so that horizontal movement of one stud and collar does not interfere with movement of an adjacent stud and collar. The anode support can be adapted to permit movement of adjacent collars under the anodes. In addition to a stud and collar there are many means that can be devised for movably attaching the anode sections to the base plate.

It should be understood that the novelty of the instant invention does not reside in the design and construction of an anode surface, a-diaphragm, the cathode or the cell can. Any of the constructions currently in'use are acceptable and may be adapted to the present invention. The type of construction embodied in US. Pat. No. 2,987,463 is typical of the type of cell construction commercially used wherein the cathodes are in the form of parallel hollow fingers projecting horizontally from the two opposite sides of the cell can and are adapted to alternate with the anodes. The diaphragm in this type of operation is deposited upon the perforated or foraminous cathode material itself.

Movement of the anode sections results in each anode having an adjustable or variable width. This permits maximizing the gap between adjacent anodes into which the cathodes are inserted during assembly of the cell. After assembly, the gap between anode and cathode is reduced which lowers the voltage drop across the cell and improves the cell efficiency.

When the cell is assembled employing both the novel anode structure and the improved method of assembly, the minimum gap between the anode and the diaphragm is the gap required for efficient cell operation. If separate provision is made for the anode product to escape and for replenishing the anolyte such as through the anode, then the minimum gap between the anode and cathode for efficient operation is equal to the thickness of the diaphragm, rather than the previously larger gap required for assembly of the cell.

When a gap is desired for the passage of the anode products, (chlorine) and replenishing the anolyte (brine), then the minimum gap required for efficient operation of the electrolytic cell depends upon the specific design of the cell and contemplated operating conditions.

The dimensionally stable anodes which are preferred in the practice of the present invention comprise an electrically conductive surface, a material supporting said electrically conductive surface and an anode mount in contact with the material which supports the electrically-conductive surface, for mounting the anode to the cell base plate. The electrically conductive surface of the dimensionally stable anodes may be composed of any material which has a sufficiently low chlorine overvoltage and which is chemically inert to the electrolyte as well as resistant to the corrosive conditions of the cell. Typically this electrically conductive surface will be composed of platinum group metals, alloys of platinum group metals, platinum group metal oxides, mixtures of platinum group metal oxides and alloys which are mixtures of platinum group metal oxides vw'th platinum group metals.

The material which supports the electrically conductive surface generally comprises film-forming metals such as titanium, tantalum, zirconium, niobium and the like. This material can be in the form of a continuous sheet of metal or preferably in the form of perforated or foraminous metal in order to provide for replenishing of the anolyte and escape of the anode products through the anode. These film-forming metals have in common the property of being non-conductors themselves under the conditions of cell operation (an oxide of the metal quickly forms on the surface thus preventing passage of current), but being able to conduct current when an electrically conductive material is in contact with a portion of the surface of the filmforming metals.

The material which supports the electrically conductive surface is in contact with the anode mount, generally by welding. This mount portion of the anode serves to dispose the anode in the proper manner within the cell and to conduct electric current to the anode surface. The mount is preferably constructed, at least on the outer portions thereof, of a film-forming metal such as titanium or tantalum. As an alternative to using a mount consisting of solid film-forming metal, it is possible to use a copper or aluminum cored mount having a layer of film-forming metal on the outside. This is preferable because copper or aluminum are less expensive and are better conductors of electricity than the film-forming metals.

The novel anode structure is not dependent upon the particular structural material or surface characteristics of individual dimensionally stable anodes employed in making the anode structure, but the novelty resides in providing movable anode sections with respect to the cell base for varying the width of the anodes.

Preferably, the movable sections of the anodes are opposite faces or half sections of a whole anode. The anode sections are parallel to each other and mounted on a base plate in an essentially vertical position. When mounted on the base plate, each anode section is free to move parallel to the plane of the base plate when mounted in a first mode and each is rigid with respect to the base plate when mounted in a second mode.

The best mode contemplated of practicing this invention is depicted in FIGS. 2 and 3 and comprises assembling a Hooker-type cell with the novel anode structure. With reference to FIGS. 2 and 3, the construction of the Hooker-type cell comprises:

a. mounting the anode sections 16 on cell base plate by inserting anode mounts 14 through base plate slots 12 and loosely threading anode retainer nuts onto the anode mounts along with washer 22 below the base and collar 24 with gasket 26 above the base (the anode retainer nut being loose results in the first mode permitting parallel movement of the anode section with respect to the base plate);

b. adjusting the anode sections to minimize the anode width and thereby maximize the gap for insertion of the cathode assembly 28;

c. interposing smooth essentially verticle guiding and spacing members 30 between the anodes and the .diaphragm surface on the cathodes;

d. lowering the cathode assembly 28 between the anodes;

e. positioning the anode sections to obtain the gap desired between the anode and cathode;

f. tightening the anode retainer nuts 20 to fix the anode sections in the position of the desired gap; and

g. completing the assembly of the Hooker-type diaphragm cell according to conventional means.

When the desired gap (step e above) is greater than the thickness of the diaphragm, then the spacers inserted between the anode and diaphragm during step c greatly facilitates positioning the anode sections to obtain a gap equal to the combined thickness of the spacers and the diaphragm. Otherwise the spacers are removed prior to step e.

The spacer member should be constructed of a material that is essentially non-conducting and chlorine resistant under the conditions of operation of the cell or if constructed of a conducting material it must be removed after assembling the anodes and cathodes but prior to operating the cell. The spacing members must be interposed between the cathodes and anodes for at least until the anodes and cathodes are assembled and aligned with respect to each other and the gap adjusted. Preferably the spacing members are removed after the anodes and cathodes are assembled.

Spacing members are preferably constructed of cylindrical, smooth, non-conducting material shaped in the form of a candy cane with the curved part fitting over the anode or under the cathode. The preferred thickness for the spacers is between one-sixteenth inch and three-eighths inch with one-fourth inch being particularly preferred.

The preferred materials of construction of the spacing member are plastic (such as polypropylene or polyvinyl chloride), hard rubber, Teflon or other materials that are inert in the electrolytic solution. (Teflon is particularly preferred). Although inert material is preferred for the spacing member, material that decomposes during cell operation is not objectional if the decomposition products do not interfere with the operation of the cell.

What is claimed is: 1. In a multiple anode assembly for a Hooker-type diaphragm cell comprising a base plate and a plurality of essentially parallel dimensionally stable metal anodes, said anodes having anode mounts for attaching the metal anodes in an essentially perpendicular position to the base plate, the improvement which consists of each of said anodes having adjustable anode sections with independent anode mounts for each section, said anode mounts having means for providing two modes of attaching the anode section to the base plate, the first mode in which each anode section is movably attached to the base plate permitting horizontal movement of the anode sections relative to the base plate for varying the width of the anode composed of said sections, and the second mode in which each anode section is rigidly attached to the base plate. I

2. The multiple anode assembly of claim 1 in which: the base plate has a plurality of slots; the anode section mounts are threaded studs protruding through said slots having a diameter at least one thirtysecond inch smaller than said slot and having a nut on the end of the stud protruding through said slots; said first mode being achieved with the nut loosely threaded onto the stud and the second mode being achieved with the nut tightly threaded onto the stud and secured with respect to the base plate. 

1. In a multiple anode assembly for a Hooker-type diaphragm cell comprising a base plate and a plurality of essentially parallel dimensionally stable metal anodes, said anodes having anode mounts for attaching the metal anodes in an essentially perpendicular position to the base plate, the improvement which consists of each of said anodes having adjustable anode sections with independent anode mounts for each section, said anode mounts having means for providing two modes of atTaching the anode section to the base plate, the first mode in which each anode section is movably attached to the base plate permitting horizontal movement of the anode sections relative to the base plate for varying the width of the anode composed of said sections, and the second mode in which each anode section is rigidly attached to the base plate.
 2. The multiple anode assembly of claim 1 in which: the base plate has a plurality of slots; the anode section mounts are threaded studs protruding through said slots having a diameter at least one thirty-second inch smaller than said slot and having a nut on the end of the stud protruding through said slots; said first mode being achieved with the nut loosely threaded onto the stud and the second mode being achieved with the nut tightly threaded onto the stud and secured with respect to the base plate. 